I can see their logic in that.
They would probably look at the situation like this.
It could be that a gift like that was brought by someone and they could have put the recipet in the bag. Put the bag down and someone walk off with it thus it is stolen.
If someone paid by credit card, then they can say you didnt pay for it simple and the only person with a right to refund it is the one that purchased it. If done by cash then you can argue could argue you brought it.
It is really to protect them a bit more.
I know just after christmas most companies do refund things without reciepts. They do the refund or voucher's really as a thing of good will really.
But if you have one surely what you could do is give the old one away to a mate or sell it and keep the newer one? or if the new one is poorer specification give it away as a christmas prezzie, or sell it to a mate and make some cash off it.
But all they are doing is protecting themselves